This invention relates to a pattern to be used for the production of a mold by a method which involves filling a pattern with a molding material incorporating a thermosetting binding agent and a substance dielectric to microwaves and thereafter irradiating the molding material with microwaves thereby causing the molding material to cure with the heat of its own generation, and to a method for the manufacture of the pattern.
A typical method heretofore known in the production of a mold has used a procedure which comprises forming a pattern of a metallic material, heating this pattern, then spraying a powdered facing agent on the surface of the heated pattern thereby covering the surface with an applied coat of the facing agent about 0.4 mm in thickness, further applying thereto a molding material containing a thermosetting resin, curing the applied coat of the molding material with the heat transferred through the metallic pattern, and thereafter separating the pattern to release the produced mold. By this method can be produced a mold of good casting surface enjoying the same accuracy as the surface of a metallic pattern. This method, however, necessitates application of heat to the pattern and inevitably entails preparation of an expensive metallic pattern. The pattern, therefore, is costly and difficult to produce. This method has an additional disadvantage that since the molding material is cured with the heat transferred through the metallic pattern, the loss of energy is heavy and the efficiency of the use of energy is inferior. Besides, since this method uses a powdered facing agent, the application of the facing agent becomes difficult when the metallic pattern has a complicated contour. Moreover since the facing agent is required to be applied substantially perpendicularly to the surface of the metallic pattern, there must be used a coating device designed exclusively to that end. These also constitute disadvantages of the method under discussion.
A suggestion offered for the elimination of these disadvantages is found in U.S. patent application Ser. No. 237,767 filed on Feb. 24, 1981. The method for producing a mold covered by this U.S. patent application uses a procedure which comprises forming a pattern with a material such as silicone rubber or ceramics permitting ready passage of microwaves and yet possessing proper degrees of elasticity and thermal resistance, applying a facing agent to the surface of the pattern, then filling this pattern with a molding material incorporating a thermosetting binding agent and a substance dielectric to microwaves, and irradiating the molding material with microwaves thereby causing the dielectric substance contained in the molding material to generate heat and consequently enabling the binding agent to be cured with the heat.
Patterns to be used for the production of molds as by the method described above have been suggested in U.S. patent application Ser. No. 269,967 filed on June 3, 1981, for example. The patterns which are disclosed in this U.S. patent application include a pattern which has a front layer of silicone rubber or fluororubber lined with a rear layer consisting of thermally insulating, rigid styrene resin, acrylic resin, or epoxy resin sparingly susceptible to loss of microwave energy and glass fibers or ceramic substance and a pattern which has a matrix of inexpensive and easily moldable dry wood, synthetic wood, epoxy resin, or acrylic resin and a thin film of silicone rubber of fluororubber applied to the surface of the matrix, for example.
The conventional patterns mentioned above, however, have inevitably proved expensive because their manufacture entails much time and labor. Further because of their bulkiness, these patterns weigh much and it is difficult to handle them.
Moreover, owing to relatively poor strength, they have readily sustained breakage during use.